Marvel Studios originally didn't have plans to use Nick Fury again after future for Samuel L. Jackson's Nick Fury wasn't guaranteed at that point.
The Iron Man post-credits scene showed Nick Fury paying Tony Stark (Robert Downey Jr.) a surprise appearance in his house. Fury discussed Tony's "I am Iron Man" confession and how he's just unknowingly become part of a bigger universe. Fury then brought up the Avengers Initiative to tease that Iron Man would be part of the MCU's first Avengers team. While the Avengers assembled a few years later, the scene also established Nick Fury as SHIELD's director and essential to the future. He's gone on to appear in multiple movies and was a connecting character throughout the MCU's Phase 1. It might seem as though Marvel had this all planned out, but they've itted that wasn't the case.
Nick Fury's appearance in Iron Man's post-credits scene was initially conceived without any future appearances in mind, according to The Story of Marvel Studios: The Making of the Marvel Cinematic Universe. Samuel L. Jackson agreed to do the cameo a few years after learning Fury looked just like him in the comics now, but he didn't have a deal in place to appear in future films. Marvel didn't put plans in place for more Fury either because they had no idea if general audiences would care about the tease.
"Latcham says they called Jackson and asked if he was still interested, and if so, would he do a cameo for them. ‘We didn’t have a deal with him for future movies,’ Latcham clarifies. ‘It was just this weird idea that maybe people give a shi-- if we stick it on the end’ Jackson agreed, and even if the scene didn’t amount to much at the time, the team at Marvel Studios decided it should remain as secret as possible to try and preserve a surprise for the hard-core comic fans who would get it right away."
The Captain Marvel, and Fury is still a player in Phase 4's story.
While Marvel Studios and Kevin Feige's overall plan is often discussed as a reason why the MCU has worked so well, the lack of plans for Nick Fury after Iron Man is a perfect example of how fluid the plan really is. There were even discussions of Fury teasing Spider-Man and mutants at one point. If audiences didn't care about Nick Fury or the tease of more, it's entirely possible his MCU future wouldn't have become so prominent. The response Marvel got to the scene and Iron Man overall helped secure that the MCU would go on and that Fury's tease could be paid off in the future.
